refactor(core): make KlondikeInstruction the move currency

Remove the (from, to, count) tuple as an internal move-passing wrapper.
Game logic now stays in KlondikeInstruction space end to end:

- Add GameState::apply_instruction, the native apply path. move_cards
  becomes a thin pile-coordinate adapter that converts to an instruction
  and delegates, so move bookkeeping (validation, score/recycle history,
  undo snapshot) lives in one place instead of being duplicated.
- next_auto_complete_move matches DstFoundation directly instead of
  projecting every candidate to pile coordinates.
- proptests and the storage round-trip test apply instructions directly
  rather than round-tripping instruction -> tuple -> move_cards.

The single instruction -> pile decode is renamed instruction_to_highlight
-> instruction_to_piles and kept in core: decoding a tableau run length
needs upstream pile-stack types core does not re-export, so relocating it
would duplicate the logic across engine and wasm. The two rendering edges
(engine hint highlight, wasm debug move list) call this one decoder; the
engine's hint_piles is a thin delegation to it.

Also includes the CardEntityIndex render-side index and a SelectionPlugin
init_resource fix so update_selection_highlight no longer panics in test
harnesses that omit CardPlugin.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

solitaire_engine/src/selection_plugin.rs

@@ -41,7 +41,7 @@ use solitaire_core::{Foundation, KlondikePile, Tableau};
 use solitaire_core::card::Card;
 use solitaire_core::game_state::GameState;
 
-use crate::card_plugin::CardEntity;
+use crate::card_plugin::CardEntityIndex;
 use crate::events::{InfoToastEvent, MoveRequestEvent, StateChangedEvent};
 use crate::game_plugin::GameMutation;
 use crate::input_plugin::{best_destination, best_tableau_destination_for_stack};
@@ -147,8 +147,12 @@ pub struct SelectionPlugin;
 
 impl Plugin for SelectionPlugin {
     fn build(&self, app: &mut App) {
+        // `CardEntityIndex` is owned and kept current by `CardPlugin`; this
+        // call is a no-op there. It is declared here so `update_selection_highlight`
+        // can read it via `Res<>` even in harnesses that omit `CardPlugin`.
         app.init_resource::<SelectionState>()
             .init_resource::<KeyboardDragState>()
+            .init_resource::<CardEntityIndex>()
             .add_systems(
                 Update,
                 (
@@ -657,7 +661,7 @@ fn update_selection_highlight(
     kbd_drag: Res<KeyboardDragState>,
     game: Res<GameStateResource>,
     layout: Option<Res<LayoutResource>>,
-    card_entities: Query<(Entity, &CardEntity)>,
+    card_index: Res<CardEntityIndex>,
     highlights: Query<Entity, With<SelectionHighlight>>,
 ) {
     // Always despawn any existing highlight first.
@@ -695,7 +699,7 @@ fn update_selection_highlight(
     {
         spawn_highlight_on_card(
             &mut commands,
-            &card_entities,
+            &card_index,
             &card,
             card_size,
             source_color,
@@ -712,7 +716,7 @@ fn update_selection_highlight(
         if let Some(card) = top_face_up_card(dest, &game.0) {
             spawn_highlight_on_card(
                 &mut commands,
-                &card_entities,
+                &card_index,
                 &card,
                 card_size,
                 dest_color,
@@ -741,27 +745,24 @@ fn pile_cards(game: &GameState, pile: &KlondikePile) -> Vec<(Card, bool)> {
 /// the matching `CardEntity::card`. No-op if no entity matches.
 fn spawn_highlight_on_card(
     commands: &mut Commands,
-    card_entities: &Query<(Entity, &CardEntity)>,
+    card_index: &CardEntityIndex,
     card: &Card,
     card_size: Vec2,
     color: Color,
 ) {
-    for (entity, card_entity) in card_entities {
-        if card_entity.card == *card {
-            commands.entity(entity).with_children(|b| {
-                b.spawn((
-                    SelectionHighlight,
-                    Sprite {
-                        color,
-                        custom_size: Some(card_size + Vec2::splat(4.0)),
-                        ..default()
-                    },
-                    Transform::from_xyz(0.0, 0.0, -0.01),
-                    Visibility::default(),
-                ));
-            });
-            break;
-        }
+    if let Some(entity) = card_index.get(card) {
+        commands.entity(entity).with_children(|b| {
+            b.spawn((
+                SelectionHighlight,
+                Sprite {
+                    color,
+                    custom_size: Some(card_size + Vec2::splat(4.0)),
+                    ..default()
+                },
+                Transform::from_xyz(0.0, 0.0, -0.01),
+                Visibility::default(),
+            ));
+        });
     }
 }